Process and device for synthesis gas generation with carbon dioxide return

The invention relates to a method for producing a carbon monoxide and

Hydrogen-containing synthesis gas, with natural gas having a first

Carbon dioxide partial pressure (C0 2 is provided pressure) and, among other things processed by increasing the pressure in a natural gas-use for a thermochemical conversion, in which a synthesis gas with a C0 to the first 2 -pressure lying second C0 2 produced -pressure, following from the at least carbon dioxide is separated in order to obtain the synthesis gas and carbon dioxide, of which at least a part

returned and used in the thermochemical conversion of the natural gas input.

The invention also relates to a device for performing the

method according to the invention.

Synthesis gases containing carbon monoxide and hydrogen are mainly produced from natural gas by autothermal reforming (ATR), partial oxidation (POX),

Steam reforming (SMR) or combinations of these methods, which have been known from the prior art for many years, are generated. The natural gas is processed into a natural gas feed through desulphurisation, heating and compression, which is then thermochemically converted into a crude synthesis gas which, in addition to carbon monoxide and hydrogen, also contains a large amount of carbon dioxide as well as water and other substances undesirable in the synthesis gas. The

Crude synthesis gas, the pressure of which essentially corresponds to the pressure of the natural gas feed, is therefore subjected to several separation steps in order to obtain the synthesis gas in the required composition.

It is known from the prior art to separate carbon dioxide from the raw synthesis gas, to recycle it and to use it when converting the natural gas input. The returned carbon dioxide is converted with hydrogen to carbon monoxide and water or with elemental carbon to carbon monoxide, which increases the carbon monoxide content in the raw synthesis gas.

In order to separate off carbon dioxide, the raw synthesis gas is subjected to gas scrubbing, in which the carbon dioxide is absorbed by a scrubbing agent, which is charged with carbon dioxide. The pressure of the loaded scrubbing agent is then lowered in order to desorb carbon dioxide, so that in addition to regenerated scrubbing agent for renewed use in gas scrubbing, carbon dioxide is obtained at a pressure that is significantly below the pressure of the crude synthesis gas or the natural gas input.

Gas scrubbing suitable for separating carbon dioxide from raw synthesis gases, such as methanol or amine scrubbing, causes high investment and operating costs and for this reason alone has a negative effect on the profitability of the

Synthesis gas generation from. If the carbon dioxide obtained in the gas scrubbing process is fed back and used in the conversion of the natural gas input, the expenditure on equipment and energy required for the necessary carbon dioxide compression has an additional adverse effect on economic viability.

The object of the present invention is therefore to provide a method of the generic type and a device for carrying it out which are suitable for overcoming the disadvantages of the prior art described and which

To increase the profitability of synthesis gas production.

In terms of the method, the object is achieved according to the invention in that the raw synthesis gas for separating off carbon dioxide is retentate on the retentate side via a for

Carbon dioxide permeable membrane is performed, which is flushed permeate side by the provided natural gas.

The separation of carbon dioxide from a carbon dioxide-containing gas mixture with the aid of a membrane has long been state of the art. A membrane suitable for this has a high level of permeability and selectivity for

Carbon dioxide on while it is for all or at least most of the rest

Components is either impermeable or has a significantly lower permeability. On the permeate side of the membrane, the separated carbon dioxide can therefore be obtained in a permeate stream, while the remaining components of the gas mixture are drawn off as a retentate stream from the other, the retentate side of the membrane.

In addition to the material properties, the thickness and the cross-sectional area of ​​the membrane, the difference between the C0 2 pressures on the retentate and permeate side is decisive for the level of permeability . The bigger this one

Difference is, the higher the permeability and the more effective it can be

Carbon dioxide can be separated from the carbon dioxide-containing gas mixture. In order to prevent this pressure difference from being reduced by the accumulation of carbon dioxide on the permeate side, the permeate side is coated with a purge gas that has a low C0 2 pressure.

Due to the different C0 2 pressures in the natural gas provided and the raw synthesis gas, at least part of the carbon dioxide present in the raw synthesis gas is separated and passes through the membrane directly into the natural gas provided, with which it is carried on and processed for use with natural gas. In particular, the carbon dioxide separated off via the membrane is compressed together with the natural gas, so that it is not necessary to use a separate carbon dioxide compressor for its return.

The method according to the invention is all the more effective, the more the C0 2 pressures of the two gas streams differ. The C0 2 pressure is sensible in the

Raw synthesis gas is at least 10 times greater than the C0 2 pressure in the natural gas.

For the separation of carbon dioxide from the raw synthesis gas, a membrane is expediently used which has a high level of permeability for carbon dioxide, but which does not allow other components present in the raw synthesis gas to pass through, or allows it to pass much worse, so that carbon dioxide is largely separated selectively from the raw synthesis gas.

Depending on the sulfur content of the natural gas provided and that for the

Conversion of the natural gas use method used, a

Desulfurization step may be necessary when processing the natural gas provided. The sulfur is hydrogenated to hydrogen sulfide, which is then removed by adsorption. According to the state of the art, the hydrogen required for the hydrogenation is separated from the raw synthesis gas, for example by pressure swing adsorption, and mixed with the natural gas to be processed.

If the natural gas is at a higher pressure than the returned hydrogen, the hydrogen must be compressed.

One embodiment of the method according to the invention, however, provides for the raw synthesis gas to be passed over a membrane which is permeable not only to carbon dioxide but also to hydrogen, so that carbon dioxide and hydrogen are largely separated selectively from the raw synthesis gas. The membrane expediently allows hydrogen to pass through in an amount that allows at least the hydrogenation of some of the sulfur components that are present in the natural gas provided and used as flushing gas on the permeate side of the membrane.

It makes sense to choose the membrane so that no more than that for the

Hydrogenation of the sulfur components required amount of hydrogen passes through the membrane into the provided natural gas.

The crude synthesis gas, which is depleted in carbon dioxide content via the membrane and withdrawn as a retentate stream, will usually not meet the purity requirements placed on the synthesis gas. In particular, its carbon dioxide content will be too high, so that the crude synthesis gas for a further separation step

Must be subjected to carbon dioxide removal. Is the production of

With carbon monoxide in the foreground in the production of synthesis gas, an expedient embodiment of the method according to the invention provides for the carbon dioxide obtained in the further separation step to be returned to the thermochemical conversion of the natural gas input. The raw synthesis gas with its carbon dioxide content depleted is preferably fed to an acid gas scrubber in order to

To separate carbon dioxide as completely as possible and to win largely selectively.

Preferably, however, the entire amount of carbon dioxide to be returned for the generation of the raw synthesis gas is separated from the raw synthesis gas via the membrane, so that none of the carbon dioxide downstream of the membrane may still be removed from the

Carbon dioxide to be separated off synthesis raw gas needs to be recycled in a costly manner and can be used elsewhere.

The method according to the invention is used with particular preference when the use of natural gas is converted by steam reforming. However, the use of the process is also advantageous if the crude synthesis gas is through

Partial oxidation, autothermal reforming or another thermochemical conversion process is obtained.

The invention also relates to a device for generating a synthesis gas containing carbon monoxide and hydrogen, with a compressor

Comprehensive processing device for processing a natural gas provided with a first carbon dioxide partial pressure (C0 2 pressure) to a natural gas insert, a converter in which the natural gas insert can be converted thermochemically to a crude synthesis gas, which has a higher than the first C0 2 - Pressure lying second C0 2 pressure, and a separation device in which the synthesis gas from the synthesis gas at least by the separation of

Carbon dioxide is obtainable, the separation device being connected to the converter in such a way that carbon dioxide separated from the raw synthesis gas

returned and can be used in the thermochemical conversion of the natural gas input.

The object is achieved according to the invention on the device side in that the processing device is connected to the separation device via a membrane module which has a membrane that is permeable to carbon dioxide and to which the crude synthesis gas can be fed on the retentate side, while the natural gas provided can be used as a purge gas on the permeate side.

The membrane is preferably permeable to carbon dioxide, while it is practically impermeable to the other substances present in the raw synthesis gas. In one embodiment of the invention, the membrane is not only permeable to carbon dioxide, but also to hydrogen, while it is permeable to the rest of the

Raw synthesis gas present substances is practically impermeable.

The membrane that is permeable to carbon dioxide is preferably made of a rubber-like or glass-like polymer material, as is known from the prior art. It can also be constructed as a composite membrane in which active components such as amine groups improve the selectivity.

In addition to the membrane module, the separating device can have a further, downstream of the membrane module and with the converter

Have fluidically connected device for separating carbon dioxide from the raw synthesis gas, so that more carbon dioxide from the

Crude synthesis gas can be separated and returned to the converter. This device is preferably an acid gas scrubber, with which carbon dioxide is largely completely extracted from the carbon dioxide content depleted

Crude synthesis gas removed and largely selectively obtained.

The thermochemical converter can be any type of reactor that is known from the prior art for use in the production of synthesis gas from natural gas. It is preferably the thermochemical one

Converter, however, to a steam reformer, an autothermal reformer or a POX reactor.

In the following, the invention will be explained in more detail using an exemplary embodiment shown schematically in FIG.

FIG. 1 shows the invention in a first and a second preferred variant.

In both preferred variants, natural gas is provided via line 1 in order to convert it into a raw synthesis gas 2 containing hydrogen and carbon monoxide, in which carbon dioxide is present at a higher partial pressure than in the natural gas 1 provided. Both the natural gas 1 and the raw synthesis gas 2 provided are in the membrane module Z is initiated, in which a membrane M which is selectively permeable to carbon dioxide is arranged, the retentate side of which is coated by the raw synthesis gas 2 and the permeate side of the natural gas 1 provided. Due to its higher partial pressure on the permeate side, carbon dioxide 3 is separated from the raw synthesis gas 2 via the membrane M and converted into the natural gas 1, which acts as a flushing gas and which leaves the membrane module Z via line 4 enriched with carbon dioxide. In the processing device A, the natural gas 4 enriched with carbon dioxide is first compressed by the compressor P and then fed to the desulfurization device E via line 5 in order to obtain a largely sulfur-free natural gas feed 6. Together with steam 7, the natural gas feed 6 is fed to the converter K, which is, for example, an SMR or an ATR reactor, and is thermally converted to a carbon monoxide-rich synthesis crude gas 8 containing hydrogen, water and carbon dioxide, which after cooling and the removal of water from the arranged in the separator T. in order to obtain a largely sulfur-free natural gas feed 6. Together with steam 7, the natural gas feed 6 is fed to the converter K, which is, for example, an SMR or an ATR reactor, and is thermally converted to a carbon monoxide-rich synthesis crude gas 8 containing hydrogen, water and carbon dioxide, which after cooling and the removal of water from the arranged in the separator T. in order to obtain a largely sulfur-free natural gas feed 6. Together with steam 7, the natural gas feed 6 is fed to the converter K, which is, for example, an SMR or an ATR reactor, and is thermally converted to a carbon monoxide-rich synthesis crude gas 8 containing hydrogen, water and carbon dioxide, which after cooling and the removal of water from the arranged in the separator T.

Cooling device C is passed into membrane module Z via line 2 for separating carbon dioxide. From the raw synthesis gas 9, which is depleted in carbon dioxide content, the synthesis gas 10, which consists largely of hydrogen and carbon monoxide, is finally obtained in the acid gas scrubber S, in particular through the removal of remaining carbon dioxide.

In order to increase the carbon monoxide content in the synthesis gas 10, in the second preferred variant of the invention the carbon dioxide 11 separated from the raw synthesis gas 8, which is depleted in carbon dioxide content, is compressed via the compressor P ' and then via line 12 the natural gas already enriched with carbon dioxide 4 mixed in.

WE CLAIM

1. A method for producing a synthesis gas (10) containing carbon monoxide and hydrogen, wherein natural gas (1) is provided with a first carbon dioxide partial pressure (CC> 2 pressure) and, inter alia, by increasing the pressure (P) to a natural gas insert (6) for a thermochemical conversion (K) is prepared, in which a synthesis gas (2) with an over the first C0 2 -pressure lying second C0 2 produced pressure, is separated from the below at least carbon dioxide (3, 1: 1), to the synthesis gas (9) as well as obtaining carbon dioxide, at least part of which is recycled and used in the thermochemical

Conversion of the natural gas insert (6) is used, thereby

characterized in that the crude synthesis gas (2) for the separation of carbon dioxide on the retentate side is passed over a membrane (M) permeable to carbon dioxide, which is flushed on the permeate side by the natural gas (1) provided.

2. The method according to claim 1, characterized in that carbon dioxide is separated largely selectively from the raw synthesis gas (2) via the membrane (M).

3. The method according to claim 1, characterized in that carbon dioxide and hydrogen are largely selectively separated from the synthesis raw gas (2) via the membrane (M).

4. The method according to any one of claims 1 to 3, characterized in that the thermal conversion (K) of the natural gas insert (6) takes place by steam reforming or autothermal reforming or partial oxidation.

5. Apparatus for generating a synthesis gas (10) containing carbon monoxide and hydrogen, with one comprising a compressor (P)

Processing device (A) for processing one with a first

Carbon dioxide partial pressure (C0 2 pressure) provided natural gas (1) to a natural gas insert (6), a converter (K) in which the natural gas insert (6) can be thermochemically converted to a crude synthesis gas (2) obtained, the first one over C0 2 -pressure lying second C0 2 has pressure, and a separating device (T), in which the synthesis gas (10) from the

Raw synthesis gas (2) can at least be obtained by separating off carbon dioxide (3, 1 1), the separation device (T) being connected to the converter (K) in such a way that carbon dioxide (3, 1 1) separated from the raw synthesis gas (2)

returned and can be used in the thermochemical conversion of the natural gas feed (6), characterized in that the

Processing device (A) with the separation device (T) via a

Membrane module (Z) is connected, which has a largely carbon dioxide-permeable membrane (M) to which the raw synthesis gas (2) can be fed on the retentate side, while the natural gas (1) provided on the permeate side can be used as flushing gas.

6. The device according to claim 5, characterized in that the membrane (M) is largely selectively permeable to carbon dioxide.

7. The device according to claim 5, characterized in that the membrane (M) for

Carbon dioxide and hydrogen are largely selectively permeable.

8. Device according to one of claims 5 to 7, characterized in that the membrane (M) consists of a rubber or glass-like polymer material or is constructed as a composite membrane with active components.

9. Device according to one of claims 5 to 7, characterized in that the thermal converter (K) is a steam reformer or an autothermal reformer or a POX reactor.